HUMANLACTATION 2Maternal andEnvironmentalFactors

Edited byMargit Hamosh~1'fIItOWlf Ulfi_ty M<tiiazl CartrWomitr/ItOlf. D.C.

andArmond S. GoldmanUlfivonity of TemrGt/\1GlOlf. Temr

Plenum Press • New York and London

6121 .,

Library of Congress Cataloging in Publication Data

lntemlllional Worlahop on Matomal-Environmental Factors in Human Lactation(l9g6: Oaxaca, Mexico)Human !al:wion 20

"Proceedings of an lntomational Worlahop on Matomal-Envirnnmental Factors inHuman Lactation. helli January 1$-19, 1986 in Oaxaca, Mexico' - T.p. vena.

lncIulies bibliographies ana inliex.1. Breast fceliing-Congresses.l. Breast fceliing-em.s-eultural stuliies-Congres:s·

os. 3. Lactation-Congresses. 4. Mnth....Nuttitinn-Congresses. I. Hamnsh. Margit.U. Oolclman. Armonli S. ill. Titl.. IV. Title: HUinan lactatinn two. [DNLM: I. BreastFceliing-co~.l. Lactation-congresses. 3. Milk, Human-congresses. wP 82S1613h 1986]RJ216•.1$8 1986 363.8'2 86-20$37ISBN ()'306-42389-8

Prncceliinp of an International Workshop on :-.tatemal-Environmental Factorsin Human Lactation. helli JanUatY 1$-19, 1986. in Oaxaca. Mexico

© 1986 Plenum Press. New YorkA Division of Plenum Publishing Corporation233 Spring Street, New York. N.Y. 10013

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6121 *

FEEDING '!liE PREIIAXURE INFANT: MEnlODS TO ASSESS LACTAXION PERFOIllfAllCE

Cutberto Garza, Richard Schanler, Judy Hopkinson, GarySilber, Kathleen Motil, David Hachey, Nancy Butte, andEdward Emken 1

INTRODUCTION

USDA/ASS Children's NutriCion Re.earch CenterDepartmant of Pediatric., Baylor College ofMad icine and Texas Children'. Rospical', Houston, TXC1USDA/ARS, Northern Regional Research Center,

Peoria, IL 61604)

The potential nutricional and imDUDologic benefic. of human milkco.p~ise the basis for lea use in the feeding of premature infants. Theprevailing consensus is that premature infane. should be provided milkfrna cheir mothers. Early milk produced by women who deliver premacurelyi. likely to be more appropriata nutritionally, and perhapstm.unologically, Chan is milk fra- later stages of lactacion or milkproduced by wanen who deliver at terM. Tha implementation of chi.recomaendatiaa is complicated, however, by limits in the understanding ofbasic lactation physiology. '

Nutrient Compo.icion of Milk

Numerous studies have investigated the composition of milk~ producedby women who deliver at term or premacurely (l-6). Difference. io theconcenCration. of protein, fat, na, Mg, Ca, P, and Fe have been reportedbeCween preeerm and terM milk.. Although most inve.tigators agree thatthe concentrations of protein and Na are higher in the milk. of W01IIen whodeliver prematurely, Chere i. le.a accord regarding relative and absolueediffereaces in the concentracions of the other nutrients. The lack ofagreement may result, in part, fr~ the dec~eases ia the concentrations ofmany nutrient' as lactation progresses. Published data on this copic aredifficult to interpret because of complicated perceptions of the manner tnwhich nutrient concentraeions are regulated. For example, stimulation tothe mammary gland and maternal endocrine changes in the earLy postpartumperiod are anticipated to have interactive effects on the secretions ofthe mammary gland, yet specific interactions remain obscure. In addition,there are at least four sources of variability in nutrient concentrationswhich are of concern: within day, between day, interindividual, andexperimental. Although exceptions exist, mast published estimates of thevariability of nutrient concentracions do not partition observedvariabilities (7,8). There are few insights regarding the basis of thisv~riability other than experimentaL error.

ImmunOlogic Composition of Milk

the immunologic composition of milk produced by women who deliverprematurely also LS distinct ·from that of women who deliver aC· term (9).

253

In a longitudinal study (10) of the effect of prematurity on selectedimmune components in human milk, we found that the mean concentrations oflactofer~in, lysozyme, and SIgA were higher in prete~ ~ilk. The patternsof change as laceacion progressed were similar to those observed in termmilk for laccoferrin and lysozyme concentrations. The concentration oftotal and secretory IgA, however, rose linearly during the sixth throughthe cwelfth week in pre term milk, but did not change in term milk duringthe s...... period. The significance of these differences is unknown. !heduration of pregnancy and laceation appears to be important in theregulation of the immunologic systl!lll of human milk. Conditions which.initi~tB premature delivery, the incomplete maturation of the biochemicaland endocrine changes associated with te~ pregnancy, or differences inthe management of lactation (e.g., absence of a suckling infant andduration and frequency of milk expression) may each be important in theregulation of L==une campoaents in prete~ milk.

Practical Concerns

Feeding matarnal milk as opposed to donor milk to the prematureinfant rsquires that sufficient milk of aD appropriata composition beproduced to _at the infant's nutritional needs. Fev data are available,hovaver, that evaluace lactation perfo~nce ia women who deliverpr.....tur.. ly. !he r_ind..r of this discussion will identify ....asures of •lactation p.rfQ~ttcB and describe techniques used in our laboratories to1) aid in the quantitation of rslationshipe b..tween laceadon performanceand specific strategies to initiate and maineain lactation, 2) provide animproved understanding of the factors that regulata milk composition, and3) evaluate the ..ff..ces of laccation on mat..rnal well-being.

MEAStlllES OF LAC'l:AtI01l' PEllFOlllWlC!

Milk Volume and Composition

Lactation performance may be evaluatsd frOlll the quantity snd qualityof milk that is produced, the infant's growem or the duration that anexcluaively brust-fed infant maintains a normal growth pati:ern, and theeffeces of lac cation on maternal well-b..ing. Of these param.. tars, dailymilk vol~ may be th. =ost sen8itive indicator of lactation performance(11). this judgment is based on the apparent stability of the grosscompoeition of milk from women with widely differing diets and energystores. In contrast, a falling or inadequate milk volume more commonly isrecognized as an early indicacor of.subapcimal lactation perfo~nce inwOllUln with a ursinal or inadequate llutritional status. Although detailedstudies may identify subtle changes in milk composition when milk volumesappear inadaquace, available data suggest that afcer the third or fourthmonth of lactation, gross changes in human milk composition no~lly occuronly after the initiation of glandular involution. An improvedunderstanding of the regulation of milk cOlllposition will help assess thevalidity of this hypothesis.

Infant Growth

Measures of lactation perfo~nce that ~ely on infant growth aredifficult co use because of unresolved questions about the adequacy ofa.vailable growth sta.ndards, characteristics of "not"mal 1t growth patterns inhuman milk-fed infants, inferences which may be drawn from cross-sectionalvs longitudinal approaches Co the analysis of growth data., and influencesother than diet on growth (12). These issues will not be discussedfurther.

254

Maternal Well-being

There is very lic~le information available about the effects oflactation an maternal well-being. Most reported studies have dealt withissues of either maternal fereilicy or body composition. A few studiesbave addressed the effects of lactation on maternal bone mineral status(13,14). the need for more functional asses.....nts is clear.

PllXLIHINARY FIIIIlDlGS OF RECENT SWDIES ASSESSDlG LACTATION PERFORMANCE

Milk Volume and Lactation Management

Factors expected to influence lactation performance includereproductive bistory, diet and nutrient stores, length of pregnancy,physiologic maturation of the lIIlIlIIIII&ry gland during pregnancy and afterdelivery, feeding behaviors of the infant, general maternal physiologic.tatus (e.g., maternal age, p.ychological .tress, illness, and livingconditions), individual characteristic. (e.g., genetic make-up andendocrine-diet response.), and lactation management. In che absence ofthe .tilllulacion provided normally by a .uckling infant, lactationmanagement takes an added importance because the frequency and duration ofmilk expre.sion are determined solely by che mother.

\;e have estimated the effect. of frequency and duration of milkexpression an lactation performance in women who deliver prematurely.thirty-five _en who delivered healthy, appropriate for gestational age,VLBW infant. between 28 and 30 week. ge.tation were enrolled (15). theclinicsl caur.e of these infant. has been reported (16). two of the 35women ....re excluded frClll the.e prelilllinary analyses because of failure ·cocamply with protocol requir......nt.. Subject. were enrolled within 1 weekof delivery, provided with an EgneU breast PUlllt' (Ega..ll, I"",., Cary II.),and aided in lactation manag......nt by a .upporc Cem based in the hospicalcaring for their iufanc$.

Generally, .ubjeccs were asked to e=pty boCh breasts 6 to 8 cimes perday. The .ubjects recorded Che time and duracion of milk expression andthe volWlle of milk expressed for up co 60 days after delivery. twenty-cwoWGIIIeQ also provided 24-hr pools of milk. An aliquoC of the 24-hr pool wasreserved weekly for nutrient and immunologic analy.es. twenty-foue-hourvolumes of milk eolleeced at 15 and 30 day. have been regre.sed againstthe ince"_l between delivery and the initiation of milk expression anaChe daily frequency and duration of milk expression. Parity, gravidiey,p'J:iQJ:' tuu·sing experieac8, -and ~ce:-l1al age also have been. examined fol:'their associations with milk volume.

Milk volume on day 15 (r • -0.44, p < 0.02), buc nat day 30, liascorrelated negatively with the interval between delivery and initiation ofmilk expression. the change in mill< volume between days 15 and 30 II&S

related significantlY to the average frequency of milk. expressiQn betweenday l5 and 30 (AVol • -344 .. 68.5 [frequency/day]) and cha daily averageduracion of PUlllt' use during ehe same interval <A Val· -76.8 .. 1.24(v min/24 hour.}). the change in daily frequency of milk expressionbecween days 15 and 30 was relaced posicively co Che net change in ~ilk

volume during this incervsl (A Val • 35.1 .. 76.1 (frequency / daY] ). Maternalage also correLaced positively with the change in milk volume during Cheindicated interval. Whether maternal age is a significant variable ehatis independent of parity, gravidiey, and previous breastfeeding experienceremains to be determined.

255

The relative efficacy of altering ~ilk volume by changing either thefrequency or duration of milk expression can be approximated cautiouslyfrom these relationships if one accounts for the mean duration of a singlemilk expression, approximately 20 minutes. the regression coefficientsrelating these management variables to the change in milk volume susgestthat a change in the frequency of milk expression is approximately twa tothree times more effective in altering milk volume than is a change in theduration of milk eXpression. Importantly, adverse effeces on milk volumedue to delays in initiating milk expression can be OVerCome more easily byincreasing the frequency of milk expression than by i.ncreasing theduration of. milk expression. Additional studies are needed to determinewhether changes in milk volume can be achieved by increases in thefrequency of milk expression even if the breast is not emptied each ~ime

..ilk is expressed. Although changes in milk volume were related to· thesemanagement: variables., significant: ralat:iol1ships seldom ware observedbetveen the variables and the absolute volume of milk produced.

Although Ulllltiple endocrine factors are likely contributors to theregulation of milk production, prolactin is believed to be the principalmadiato~ of the positive associatiou becweeu milk volume and the frequencyof milk expres5iou. Most available data- nave been obtained in subjectswho delivered te~ infants; however, si=ilar re5~onses are likely in womenwho daliver pr.....turely. PostpartWII prolactin levels fall rapidly inWC1IUIIl who feed their infants less than four to six times per day (17).The fall in p~olactin levels appears mast exaggerated in ..omen who adoptthis infrequent pattern of feeding during the first three ~onths oflactatioll.

RegUlation of Milk Composition

Milk voluma can be altered Substantially by changes in lactationmanagement; milk composition, however, appear3 aIOrl!l seabls. The effecesof diet; for example, all milk c01llposition call be sUllllll&ri::ed briefly (18).Tha consequences of dieea:, vita=in intakes are variable; thecoucencracioDs of water soluble vitamins appea~ to be influenced by recentdietary intake IDOre easily than those of minerals and fat-solublevitamins. '!'he conc8ntratiollS of p~ocein l1itroge:n, lactose, and fatgenarally are less responsive to broad differences in diet, although thelevels of specific milk proteins may be influanced by the amount ofdietary protein (19). In contrast, alterations in the dietary pattern orcontent of fatty acids and carbohydrates will influence markedly the fatryacid camposition of human milk (20). !he piccure of general stability inhuman milk composition is bolstered by observations of significant"tracking" of nutrient concent:rations in milks of individual women. nteconcentracions of tocal N~ procBiu N, l.ctose, fac, and calories wereobserved to cor~elace significantly (r ranged gram 0.42 to 0.74,p <0.00 with their subsequent" IDOnthly values (21). lJhen mineralconcentrations were evaluated, analogous r yalues ranged from 0.33 to 0.90for Na, K, Mg, Ca, P, and Zn (22). Correlation coefficients above 0.7were observed for Ca and Za.

We have tested ewo approaches to ident:ify factors which account fortb.is relative stability. The first: was used to evaluate the influence offeeding patterns oa- the energy concentration of milk (unpub lishedobservations).

Milk samples were collected throughout the day . from women exclusivelybreascfeeding their infants on demand. Subjects gave birth to term,healtby infant:s; the cnaracterist:ics of these subjects have been reported(23). Subjects were followed monthly for the firs. four ~onths oflactation. At each nursing over a 24-hr period, infants were offered one

256

breast and milk was expressed from ~he other using an Egnell electricalbreast pump. Subjects were asked not to exceed 15 minutes of pumping andCo scop sooner if milk flow were reduced markedly. Feeding and pumpingwere done at alternate breases at successive nursings. The gross energycontent of milk was determined in an adiabatic bomb calorimeter (ParrInstruments, Moline, IL). As has been reported by ochers (Z4, Z5) wefound linear (p < O.Oll and quadratic (p < 0.07> crends when the- energycontent: nf milk was regressed against che cilllll of day at which Che ..ilkwas collected. !n our st:ody populacion, the mean energy content (kcal/L)of milk Cended co increase chroughout Che day with Che lowest valuesobserved in the early I1lOrning.. The energy content of milk, however, wasrelaced negatively co Che volume of IOilk Chat was expressed and to Chetime inte:val preceding each milk expression. Fur'Chermore, the timeinterval preceding each milk expression was correlated positively with thevolume of milk expresaed. The opposice effeccs of cima lapse on chevolume and energy concent of milk probably resulc fram che synchesisand/or secretion of fat. Lactose, the other major caloric constituent inhuman milk, is unlikely to be responsible because its osmotic rolerequires that its prodw: tion and secretion be related closely to volume(Z6) •

Further exploration of the dietary and mammary physiologic factorschat regu14ce milk volume and f4t cont:ent are required before theserelacionships may be underst:ood adequately. !n col14boracion wich Dr.M.II.. Thomas, we have addressed this probl... by assessing fat: cral1spore Coche ma1llllary gland and synthesis and cral1s11ort: of fac by Che mammary gland.tlolO preliminary experiments have been conduceed (Z7-Z9). The firseinvolved ebe oral adminiseraeiol1 of ebree deuceriu=-labeled criglycerides,cripalmicin-9-l0-2HZ, criolein-l4, l4, lS, l5, l7, lS-2H6, al1dcrilinalein-lS, 15, 16, l6, -294 (Z6). Milk and blood samples werecollected fram 3 wamen- for 72 hours at specified incervals afcer thetagestion-of the labeled criglycerides. Samples vere analy:ed by gaschromacography and gaa chromatography-mass specerametry. A lO-hour delaywas observed bel:Ween the Cast: meal and the peak occurrence of thedeuterated f4cty a~ids tn milk criglycerides (Fig. l). Ibis delay isunlikely Co be accounted for by delayed gastroincestinal absorption sincepeak criglycer1de enrichmel1ts in chylOlllicro... , very low densitylipoprot:eins, and lov densicy lipoproteins vere observed before fourhours, the esrliesc lipollrotein sampling paint:. Preliminary resulCsobtained in this experiment: suggest chat the chylomicroQ ia quantitativelythe moat important immediate 90u~ce of dieeary lipids in the mammarygl.nd. these results also support the selective conservation of palmitateZ-monoglycerides across the blood inco the alveolar lumen. Integration ofresulcs obe..ined over the 72-hr period suggests thac approximacely S Col6% of Che adminiscered label was secreCed milk.

the synthesis of faccy acids by the ~mmary gland has been exploredin preliminary experiments ucili:ing diec4ry manipul4cions (Z8) ~nd ZijZOadministracion (Z9). Fatey acid synthesis by che mammary gl4nd lSaccomplished by the usual mechanisms observed in other tissues with oueimportant exception. In mase tissues, thioesterase I terminates thegrowth of acyl chains on fatty acid synthase at facs of l6 c4rbon lengch._In cbe mammary gland, thioesterase II modifies the usual productspecificity by interacting ~ith the faeey acid synthase complex.tbioesterase II catalyzes the hydrolysis of the thioescer linkages ofmedium chain acyl moieties to the multienzyme co~lex (30). The outcomeof this modification is evident from the work of Insull ee a1. (20) an asingle lactating subjec~. When the subject consumed a fat-free diet at anenergy level approximately 1/3 above her estimated requirement, lauric andmyristic acids made up 39% of the fat on a molar basis compared with 20%when the subject was on a conventional diet. We have recently assessed

Z57

ehe effects of 5% fat, 15% protein, and 80% carbohydrate diets on ehe fatcQ~osition of milk produced by women who delivered premature infants.Subjects were placed on ehe diet 9 to 12 days following delivery. Energylevels were set at eacn subject's usual ineake unless levels were below2300 keallday, ehe IlIinilllUlll intake the protocol allowed. During thedietary period, lauric and myriscic acid concentrations rose co=pared withprediet value. (Table l).

Based on observations reported by Rittenberg and Schoenbeimer (3l),.... have conducted studies to demonstrate that IlIiddle chain-length fattyacid. secreted in IlIilk can be labeled successfully following the oraladministration of 2H20. Fat synthe.is may be evaluated by ehi. techniquebecause ehe majority of hydrogens on newly synthesi:z:ed saturated fatsappear to be derived frOlll body H20. We anticipate ehat ehe.e technique.will allow uS to explore ehe influence of maternal-diet-endocrine­lactation management relationships on the fat content of human IlIilk.

Maternal Well-being

Most aasures of lactation perfonsance focus ou either the infa.nt. 0'1:'

the milk that is prnduced. Fev studies have been directed at the effectof lactation on maternal health. We have begun such studies by obtainingba.elina data an protein kinetics in women who are not at aay apparentnutritional risk. Accordingly, 12 healthy WOlIIOIn (32) have been studied at1, S, and l2 months postpartum. Dietary protein Va• •et ae l.O g/kg/dayand dietary ......rgy intake. ware .et at maintenance level. as detamned by3-day diet records. Thi. constant diet was consumed for 7 days. Maternalmilk production was eseimated by test-weighing the infane foe a minimu= of72 consecutive hour.. At the end of the dietary ineerval, a 96-houettitrogen balance vas 'conducted and a primed, constant, intravenousinfusion of 1_13C leucine was perfoC'llla<! in the fasted .taee. Theenrichmene of 13C in plasma leucine and expired CO2 was detemned by gascbromacography-$&ss spectroma:ry aud isotope-ratio mass spectrometry,re.p....eiv..ly. When a<ljusted foe ehe .tage of lactation, significantassociations vere observed becveea. the eats of leucine incorporation incoproteins synthe.ized by ehe lIIOthee and ehe volume of milk consumed by eheinfant. Eneegy and nitrogen outputs in milk al.o WlIre related positivelyto db. rate of leucine incorporacion inco tocal body protein syuchesi:edby the lIIOther (Table 2). These initial re.ults relating maternal proteinmecabolis. to cOQvl!Ilcional iadices of lactatiQIl pe:rform.anca have:identified avenues fo~ future work. These eechniques caD be used toexplore adaptations of protein =atabolism du~ng lactation in women indistinct nutritional states.

S1lllIlARY

The current preference Co feed human ~lk to premature infants isimpeded by our inadequate undee.tanding of basic lactation phy.iology.Although SOllIe of ehe peob lems stem from a lack of knOWledge of thepremature infant's nutrient neecs, Che incomplete understanding oflD&ternal f.1.Ctors t:hac govern a1i.lk co=rposicioD and volume i.s also asignificant snortcoming. We have coaducced studies Co quantitate tnerelationships beeween milk production and specific ~nagement variables.We also have explored tracer methodologies to study the regulation of milkcomposition and tne effects of lactation on maeernal metabolism in womenwho deliver at te~ and premaeurely.

258

tnCOrpORt.tOD of Oleic Aciet-d8 into :selected.pI.....a and. milk triclY"orides

Iaolope Ratio (x 100:::)

o :u ""Tlm. (heun)

Fig. 1. !lean deueeriWll enrichlllene in lIIilk triglyceride. (-eo), eocal plasma'criglyceride. (~), aad chylomicrona (~). Rapre.aneaeive daeaobcained in 0,,", of l:he l:hr.e laccaeing WOIIIl!n are pre.eneed.

TABLE 1. wuric and llyri.eic Acid Coneene of Suman Milk Sefore andDuring Conerollad Dieeary Perioda

Subjel:e Prediec (%) Day 4 (X)

1 13 242 10 L43 7 154 11 L45 12 L7

a Expre.sed a. X eoeal fac. Change. beeveenp~edi8t and conerolled period, signi£icane atp <0.05.

259

Table 2 Relationship Becween Maternal Leucine MetaboLism and Milkl'roduc: tion

VOL· 0.51 + O.lS LI - 0.44 PPAaH • 4.1S + 0.30 LI - l.12 PPAaE • l.41 + 0.15 LI - 0.32 PPAbN • -S.44 + 0.37 LQ - 0.79 PPAo

\/he..e: Vol. Milk volUlllll (g/kg ....te..nal body wt/day)N • Milk nit..ogen (mg/kg ....ternal body we/day)t • Milk ene..gy (koal/kg maternal body wt/day)

LI • Leucine incorpo..ation ( mol/kg/h..)LQ • leucine flux ( mol/kg/h..)

PPA • time siuee delivery (months)

abop < 0.01, p < O.Ol, P < 0.02

ACKllOWLtIlGMEllTS

This ..esea..oh is suppo..ted by a oont..act (NOl-HD-2-2Sl4)f ..os the National Institutes of Sealth and by the USDA/ABSChildren's Nutrition Research Caute~, Oepar~nc ofPediaerics, Baylo.. College of Medioiue and Texas Children'sRaspital, Rauseon, 'rI. This p..ojece has been fuuded in pa..ewith Federal funds fros the tr.S. Depa..tllUlnt of Agriculeu..e,Ai..iculeu..e Resesrch Servioe unde.. Coope..aeive Ag..eementDUmb... 58-7HNI-6-l00. The oontanes of this publioation do not..oessa..ily refl.ce the views 0.. polioies o~ the u.s.Deparc=enc of Agriculture, nor does mentioQ of trade- ~S,commercial products, or organizations LDply endorsement by chaU.S. Govert:mene.

1. S.A. Atkinson, M.a. Bryan, aDd G.R. Anderson, Difference in nitrogencoacentracioQ in milk from lDOthers of term and premature infant"" .::!.:aPediae... 93:67 (l978).

2. J.A. Lemans, L. Moye, D.'eall, and. M. Simmons, Differences in thecomposition of pre tam anc1 term human milk during early lactation,Pediae... Res. l6:1l3 (1982).

3. S.A. Aekiuaon, I.C. Radde, G.W. Chance, M.S. Bryan, and G.H.Anderson, Macroaaineral content of adlk obtained during earlylactation fro= mothers of p~ture infants, Early Hum. Dev. 4:5(l980) •

4. R.J. Schanle.. and W. Oh, Composition of ; ..east ~ilk obtained f ..ommothers of premature infants a8 compared eo breast milk obtained fr~

donors, J. Pediat... 96:679 (l980).5. S.J. Gross, R.J. David, L. Bauman, and a.M. Tamarelli, Nutritional

compositioQ of =ilk produced by mothers delivering pre term, J.Pediat... 96:641 (1980). --

6; H.i. Butte, C. Ga..:a, C.A. Johnson, t.O. Smich, and B.L. Niohols,Longitudinal changes in milk composition of mothers deliveringp..eterm and term infants, Ea.. ly Hum. Dev. 9:153 (l9S4).

7. "M.F. Picciano and B..A. Guthrie, Copper, iron, and zinc contene.s ofmatu..e human milk, Am. J. Clin. Nutr. 29:242-254, 1976.

260

8. M.C. Neville, a.p. Keller, J. Seacat, C.t. Casey, J.C. Allen, and P.Archer, Studies on human lactation. t. Within-feed and beCYeen­breast variation in selected components of human milk, Am. J. Clin.Nutr. 40:635 (1984).

9. ~Groaa, a.8. Suckley, S.S. Wakii, D.C. McAllister, a.J. David,and a.G. Faix, Elevated IgA concentration in milk produced bymoehera delivered of preterM infanta, J. Pediatr. 99:389 (1981).

10. A.S. Goldman, C. Garza, S.L. Nichols, C.A. Johnson, E.O. Smith, anda.M. Goldblum, Effects of prematurity on the immunologic system inhuman. milk, J. Pediatr. 101:901 (1982).

ll. C. Gsr:a and N.F. Butta, The effeet of 1IL1lternal nutrition onlactational performance, in: "Proceedings on the Symposium onF'rontiers in Clinical Nutrition, tI N. Kretchmer, ed., Aspen Press,Rockville, Maryland (l985).

12. a.G. Whitehead and A.A. Paul, Growth charts and the assessment ofinfant feeding practices in the we.tern world and in developingcountries, Early Hum. Dev. 9:187 (1984).

13. G.M Chan, N. Ronald, P. Slater, J. 80l1is, and M.a. Thomaa, Decreasedbone mineral status in lactating adolescent mothers, J. Pediatr.10l:767 (1982).

14. P.J. Atkinson and R.H. West, Loas of skeletal calcium in lactatingwomen, J. Obatet. Gynecol. 77:555 (1970).

15. J. Hopkinson, a.J. Schanler, and C. Garza, Milk production inmothers of preterM infants, (abat:) Am. J. Clin. Nutr. 41:852(1985).

16. a.J. Schanler, C. Gar:a, and S.L. Nichols, Fortified moehers' milkfor very low bireh....ight infants: results of growth and nutrientbalance .tudies, J. Pediatr. 107:437 (1985).

17. P. Delovoye, M. Demaegd, J. Delogne-De.noeck, and C. Robyn, Theinfluence of the frequency of lWrsing and of previous lactationexperience on saru.a:a p'C'Qlacein in Laceating 'lIIOthl!u:s, J. Biosoc. ·Scf.9:447 (l977).

18. S.L. Nichols, and V. Nichols, Nutrition in pregnancy and lactation,Nut:. Ab.tr. aev. 53:259 (l983).

19. A.K. Dab and 8.a. Cams, Studies on h.....n lactation. Dietary nitrogenutilization during lactation, and distribution of nitrogen inmather'. =ilk, Br. J. Nut:. 16:65 (1962).

20. W. Insull, J. Hir.ch, '1:. James, and It.S. Abrens, Jr., The fattyacida of hUlll&O milk II: Alterations produced by IlI&nipulation ofcaloric balance and exchange of dietary facs, J. Clin. Inve.t.38:443 (1959).

21. N.F. Butte, C. Gar:a, 1t.0. S=ith, and B.L. Nichols, Human milkineaka and groven performance· of exclusively beeasc-fed infants, ~Pediatr. 104:187 (1984).

22. N.E. Sutte, C. Garza, E.O. Smith, aud B.L. Nichols, Milk and mineralintakes of 45 exclu.ively breast-fed infants, (abscr) Fed. Proc.43:667 (1984).

23. N.F. Butce, C. Garza, J .E. scuff, E.O. Smith, and S.L. Nichola,Effect of maternal diet aud body co=po.ition on lactationalperfOrMance, Am. J. Clin. Nutr. 39:296 (1984).

24. ~.E. 8ytten, Clinical and chemical .tudie. in human lactation II:Diurnal variacions in major conscituents of milk, Sr. J. Hed. 1:119(l954).

25. A. Prenti~e, A.M. Prentice, and R.G. Whitenead, Breasc-milk facconcentrations of rural African women I: Shore-te~ variationswithin individuals, Br. J. Nutr. 45:483 (1981).

26. N.J. Kuhn, D.'I:. Carrick, aud C.J. Wilde, Lactose synthe.is: thepo.sibilities of regulation, J. DaiF! Sci. 63:328 (1980).

27. D.L. Hachey, E.A. Emken, M.S. !hOIll&S, L. Brown, a.o. Adloff, C•.Garza, B.L. Nichols, and P.O. Klein, Incorporation of deuterium­labeled dietary lipids into speci£ic milk lipid fraceious of humanm.ilk, !a:. ItAbstraccs of 2nd Int. Cong: Essential Fatty Acids,"(1983).

261

28. G. Silber, J. Hopkinson, D. Hachey, and C. Car:a, Modificaeion offaety acid camposieion in human milk, (abser) Am. J. Clin. Nuer.43 :688 (1986).

29. D.L. Hachey, G. Silber, L. Brown-Booeh, W. Wong, L. Lee, C. Gar:a,and P.D. !tlein, EndogenOWl faety acid syttehesis by the mammarygland, (abstr) Am. J. Clin. Nutr. 43:687 (l986).

30. C. Gar:a and J. Hopkinson, Ruman milk syttthesis and secreeion, in:"The 'theory and. l'rac:ice of NutritiQn in Pediatrics, It R.. Grand aTnJ.L. Sutphen, eds, Butterworth, (In press 1985).

31. D. Rittenberg and a. Schoenheimer, Deuterium as an indicator in thestudy of intermediary llUltaboliSlll XI: Further studies' in thebiolosical uptake of deuterium into organic substrates, vitb specialreference to fat and cholesterol formation, J. Biol. Cham. 12l:235(1937>.

32. !t.J. Moeil, C.H. Montandon, D. Hachey, T. Boueeon, P.O. !tlein, and C.G4Ir:a, The relaeionship between whole body leucine llUlcabolism andmilk production in lactating wOIlIen (abser), Am. J. Clin. Nuer. 43:678(1986).

262